The invention relates to a camshaft timing device or internal combustion engines, which timing device is located in the crankshaft drive and adapted to adapt the angular position of the camshaft relative to the drive depending on vehicle operating conditions.
DE 196 54 926 A1 discloses a camshaft timing device which is located In the drive of a camshaft from the crankshaft of an internal combustion engine. It is arranged coaxially with the camshaft and is connected to the camshaft via a central tension screw which, in turn, forms a valve housing, receiving an axially displaceable control spool, via which the supply connections of the camshaft timing device are to be completed, depending on the position of the spool, to the hydraulically operated timing-device. The connection path runs via an annular space which is provided circumferentially on the control spool and is delimited by two annular shoulders and which, depending on the axial position of the control spool, is in communication selectively with the delivery-side or return-side passages. The return passage extends, by an annular duct, which is offset axially relative to the annular space and is delimited by an annular web n to a central drain passage of the control spool. The drain passage extends to a valve housing space, which adjoins the receiving bore for the control spool in the direction of the camshaft. It is delimited, by one end face of the control spool and receives a return spring for the control spool. The threaded part of the tension screw is screwed axially into the camshaft. A return bore, which extends through the threaded part and, via a transverse bore in the camshaft, leads to an oil-collecting space, which is formed by the oil sump of she internal combustion engine, to which the camshaft drive chain case that supports the camshaft timing device of the internal combustion engine, is connected.
Camshaft timing devices of this type are intended to permit high engine speeds and accurate valve timing with low actuating forces, and at the same time have low space requirements, providing particularly for a short construction length. These factors are also determined to a large degree by the fluid passages at the return side which return the fluid to the oil-collection sump and which are also critical, since any back pressure will affect the response time and undesirable vibrations may also occur.
The problems referred to assume increased importance when, as has already been proposed (DE 198 17 319.9-13), the camshaft timing device does not operate under excess fluid pressure from one side of the actuator, but is pressurized at both sides and therefore has to operate at the control side not with a 3/2-way valve, but with a 4/2-way valve.
In a camshaft timing device for an internal combustion engine having a camshaft driven from a driveshaft by way of a camshaft drive which is capable of advancing or retarding the camshaft and therefore the valve timing, the camshaft drive is mounted onto the camshaft by a clamping screw which has a cylindrical opening in which a valve spool is movably disposed for controlling admission of hydraulic fluid to, and its release from, the camshaft drive, the valve spool being actuated by an electromagnetic motor acting against a valve spring biasing the valve spool in one direction for controlling the operation of the hydraulic camshaft drive and the valve spool is pressure balanced for accurate positioning control thereof.
Concerning a camshaft timing device operating with a 4/2-way valve according to the invention, one possible solution in which, irrespective of the actuating direction of the control slide, forces of the working medium on the control slide spool which affect its behavior are avoided and, moreover, a simplified routing of the fluid supply line paths is achieved, along with a simplified structural set-up.
The solution according to the invention also makes it possible, to integrate the valve-side connection to the delivery-side supply connection into the valve in an advantageous way, so that, in this regard, there is no need for any additional actions on the camshaft or on the mounting of the camshaft on the camshaft bearing.
An exemplary embodiment of the invention is explained in more detail below with reference to the drawings.